1. Field of the Invention
The invention relates to the determination of dynamic response properties of fluid and semi-fluid materials. More particularly, it relates to a method and sensors which will determine these properties in situ of castable-type materials, such as rubbers and plastics, as well as pourable compositions.
2. Description of the Prior Art
In certain applications, it is desirable to determine hardening or the growth of voids or softening of a cast mass of a castable-type material. For example, any of the above changes in a cast mass of a propellant grain might lead to problems of the proper firing of motors containing such grains. Although many techniques are known for determining mechanical properties of a cast mass of particles or grains, such prior art techniques are relatively complex and must be carried out under laboratory conditions or the like.
During the storage period changes may occur in the propellant. Some propellants harden, some soften and others may harden for a while, then soften. In some instances, hardening of the propellant grain will cause failure at low temperature. In other instances, softening of the grain will cause excessive "slumping" of a standing propellant grain at higher temperatures and in still a third instance softening of the grain will reduce the resistance of the rocket to the pressures generated during firing. In other instances, the rocket motors are required to withstand dynamic loads during transportation and during firing. Changes in the properties of the propellant could affect the motor capability to withstand these required loads. Propellant movement due to imposed loads causes the grain to separate or debond at various locations which debonding can be detected by one or more properly located sensors. Thus, when it is necessary to fire the rocket motor, the presence of an undesirable amount of such separations may result in improper combustion of the propellant grain, as would the undetected presence of voids.
It is therefore desirable to test such rockets for any changes in the cast propellant prior to the time of firing such rockets.
Other compositions where properties are subject to change include urethane foams which degrade upon extended storage. It is therefore also desirable to determine the change in properties of such foams.